1. Field of the Invention
The present invention relates to an image memorizing device, and more particularly, to an image memorizing device for processing a large amount of image data such as moving pictures by using large capacity memories.
2. Related Background Art
There have been known a kind of memory which is adapted to cyclically memorize data within its storage area by linking the end address of the storage area to the start address of the same and an addressing control therefor as a so-called ring memory, and an image memorizing device for storing image signals in such a ring memory has been also known.
In the ring memory, previously memorized information cannot be protected from being overwritten by next information due to the nature of its addressing control. For example, when moving pictures are to be memorized, a previously memorized image is lost by overwriting the next image, so that non-sequential images in terms of time cannot be obtained.
Incidentally, such an image memory tends to have a larger capacity and now becomes sufficiently usable as a recording medium for moving pictures. If a solid state memory such as a dynamic random access memory is used as a recording medium for moving pictures, there are advantages, e.g., a search can be performed at a high speed; data can be readily rearranged in the memory; and data can be recorded and reproduced at an arbitrary speed.
Generally, in an image signal processing circuit for processing moving pictures by using such a large capacity image memory, a digital video signal digitally converted from an analog signal, as it is, is written into an image memory by one frame portion or a plural-frame portion. Addressing of the image memory is controlled by a timing of a synchronous signal of an image signal to be written thereinto.
Conventionally, since an addressing control of an image memory is defined by a synchronizing timing of a synchronous signal, quite a few unused portion, as indicated by hatching in FIG. 1, is produced and left useless. This unused portion may occupy an unneglectable amount depending upon the number of horizontal pixels and the number of horizontal lines.
Specifically, a memory capacity assigned to one frame portion is, for example, a capacity for (2.sup.n .times.2.sup.n) pixels, as shown in FIG. 1, which has 2.sup.n kinds of horizontal and vertical addresses, respectively. The number of scanning lines is 525 in the case of an NTSC signal and 625 in the case of a PAL signal, so that approximately 700-800 of horizontal pixels are required. Therefore, substituting 10 for n, approximately 1024 (=2.sup.10) addresses are required for the horizontal pixels.
Further, in the case of a high vision signal, substituting 11 for n, 2048 addresses are required for each of the horizontal and vertical addresses.
Thus, the unused portions as shown in FIG. 1 include an extremely large amount of address, thereby exhibiting a quite low memory using efficiency. However, unless the address is reset in the horizontal scanning line units or frame units, management of the address in a large capacity memory becomes extremely difficult.